The present invention relates to the architecture of internal combustion engines, and in particular of compression-ignition engines suitable for the propulsion of light aircraft.
Persons familiar with the design of aero engines know that a significant difference exists between the engines of small tourist or private aircraft and those of transport airplanes.
Aircraft used in transportation, whether passenger airliners or freight carriers, are almost without exception propelled by turbojet engines, of which the advantages in terms of power, range and fuel economy outstrip all other types of propulsion unit. Reciprocating engines, on the other hand, are by now limited to light aircraft (e.g. single- and twin-engined planes typically as used in tourism), their rated power being generally no higher than 400-500 HP; such planes are dependable, inexpensive to operate and well-established commercially, given that the basic design of the propulsion dates back to the prewar period.
The problem currently experienced with this second type of aircraft engine is simply that of procuring a constant and sure supply of fuel in all parts of the world; whereas jet aircraft utilize `A1` fuel (by now universally available), the reciprocating engines of light aircraft can use only a special type of gasoline (a fuel formulated with particular properties, amongst which is the ability to resist freezing in significantly sub-zero temperatures). Owing to the enormous ascendancy of the jet engine in recent times, there has been a correspondingly enormous rise in the demand for A1 jet fuel at all airports, while gasoline has become increasingly scarce, often obtainable only at a high price and with no guarantees as to its quality.
Thus, an obvious contradiction exists between the growing demand for light aircraft propelled by low power reciprocating engines (which perform well for short and medium range flights as arranged by tour operators, and for private or executive use), and the limited availability of aero-engine gasoline. An additional factor now demanding consideration is the emergence, in recent automotive technology, of diesel engines that are substantially comparable in terms of power and dependability with conventional gasoline enginesg; such a situation could hardly have been foreseen at the time when gasoline aero engines were initially designed, developed and put into mass production. Moreover, in comparison to gasoline engines, diesels currently give a flatter power-torque curve (per unit displacement, needless to say) that is better suited to and exploitable at lower running speeds; this is precisely the case with aero engines, of which the speed of rotation is necessarily dictated by the required propeller speed, i.e. 2200 . . . 2600 rpm or thereabouts. Accordingly, the need is felt by the applicant to explore the notion of equipping light aircraft with reciprocating engines affording the same features of dependability and economy as the conventional aero units commissioned hitherto, but capable of operating on jet fuel, of which the availability, quality and rational cost are assured.
The object of the present invention is therefore to provide a reciprocating propulsion unit for light aircraft, exploiting diesel construction technology and adopting an architectural approach, as regards mechanical components and air intake, that permits of running the engine on jet fuel while maintaining the safety and reliability of conventional gasoline aero engines as used hitherto.